Girls at a £20,000 a year boarding school are under investigation for turning the air blue in an explicit classroom video posted on the internet.

The pupils, thought to be aged in their young teens, reel off a string of vulgar slang words and insult a female teacher who is not present.

One of the girls at the exclusive Burgess Hill School for Girls grins as she uses the teacher's name to refer to her private parts.

They then brag about posting the footage on the internet.

The video, entitled 'Life in the Classroom', also has the tagline 'This is life at break... Burgess Hill school break slutty girl play.' It is now in the hands of teachers after it was spotted on file-sharing website YouTube.

The school last night launched an investigation and alerted the girls' parents.

Ann Aughwane, headteacher, said: "We have sanctioned an investigation and are speaking to the girls' parents.

"This is a serious incident but the girls are really only guilty of immature nonsense. Their biggest error is a lack of judgement in posting this video onto the internet.

"The school regrets very much the implication that its reputation could be damaged as a result."

The 675-pupil independent school is the top-performing school in West Sussex with a 100 per cent pass rate in GCSE exams last year.

Parents pay up to £19,785 a year to send their daughters aged between two and 18 to the school in Keymer Road.

Mrs Aughwane said the video was shot at the end of the Christmas term when "spirits were high".

She added: "We have a policy of educating rather than banning when it comes to the internet and social networking websites.

"I now have some young girls who are fully aware of the dangers of these websites. "They are absolutely horrified at the thought their actions could have damaged the school.

"We are very disappointed in them and their behaviour has been wholly inappropriate. Any punishment will be decided in due course of the investigation."

The school, which stands in a 14-acre estate close to the centre of Burgess Hill, has established itself as a centre of excellence in music, sport, art and drama.

As well as boarding girls, day pupils are ferried in by coach from Lewes, Newick, Henfield, Worthing, Crawley, East Grinstead and Hove.

The footage posted on YouTube is not the first to have led to recriminations for school pupils.

In October last year an entire class of 16 and 17-year-olds were suspended from Central Sussex College, in Crawley, after they filmed themselves bullying a teacher and posted footage on YouTube.

Earlier that year, a clip showing teenagers from the college attempting martial arts moves on each other also appeared on the site.